1. Technical Field of the Invention
The present invention relates to the formulation of particular deformable hollow particles into cosmetic and/or dermatological compositions containing titanium dioxide (nano)pigments, to reduce the photobluing initiated by the presence of said pigments and/or the whitening usually occurring when this type of composition is topically applied onto human skin. Such hollow particles exhibit a particle size ranging from 1 .mu.m to 250 .mu.m and comprise an expanded copolymer of vinylidene chloride, a (meth)acrylate and acrylonitrile.
The compositions according to the invention may, in particular, be topically applied for protecting the skin and hair against light, in the form of sunscreen compositions, as well as for makeup, care and hygiene of the skin, of the face, of the human body including the scalp and the mucosae, the hair and, lastly, for the therapeutic treatment of the skin and of the mucosae. Thus, the compositions of the invention may comprise an oil-in-water emulsion, a water-in-oil emulsion, a care cream or lotion, a balm, a blusher, a fluid or cast foundation, or a dermopharmaceutical ointment.
2. Description of the Prior Art
It is known to this art that light radiation of wavelengths of from 280 nm to 400 nm promote tanning of the human epidermis and that irradiation with wavelengths between 280 nm and 320 nm, i.e., UV-B irradiation, causes erythemas and skin burns which impair the development of the natural tan; hence, this UV-B radiation must thus be screened or blocked from the skin.
It is also known to this art that UV-A radiation, of wavelengths of from 320 nm to 400 nm, which tans the skin, also adversely affects it, especially in the case of sensitive skin or skin which is constantly exposed to solar radiation. In particular, UV-A irradiation causes a loss in skin elasticity and promotes the appearance of wrinkles, resulting in premature aging. Such irradiation promotes triggering of the erythematous reaction or amplifies this reaction in certain individuals, and may even be the source of phototoxic or photoallergic reactions. Thus, it is desirable to also screen out UV-A radiation.
A wide variety of sunscreens, inorganic pigments and organic screening agents, exist on the market for screening out UV-A and UV-B radiations. These sunscreens must be capable of absorbing or blocking the harmful rays of the sun, while at the same time remaining innocuous to the user.
Thus, many organic sunscreens capable of absorbing harmful UV irradiation more or less selectively are known to the cosmetics art. For a variety of reasons, however, these screening agents are not entirely satisfactory.
Accordingly, it is increasingly sought to avoid the use of these organic screening agents by favoring the use of inorganic pigments, which also act as sunscreens, principally by scattering/reflecting the UV, while contributing greater safety for the user.
In this respect, the inorganic pigment most widely employed to date is titanium dioxide, the screening or blocking properties of which are well known to this art.
In order to attain suitable protection factors, however, it is necessary to formulate high percentages of TiO.sub.2, in particular higher than 5% by weight, into the sunscreen compositions.
However, with such amounts of TiO.sub.2, compositions containing these pigments exhibit instability to light in an oxygen-free medium, which is manifested by the appearance of a blue coloration (photocoloring known as photobluing). Also, the appearance of whitening when these compositions are applied to the skin is observed. These two phenomena are obviously not desirable from an aesthetic standpoint.